Automatic heat control



March 19, 1935. E, WIL N 1,994,904

AUTOMATIC Q-IEATCONI'ROL Filed April 22, 1935 INVENTOR LZr/ M2500.

I ATTORNEY WITNESSES:

Patented Mar. 19, 1935 AUTOMATIC HEAT CONTROL Earl D. Wilson,Wilkinsburg, Pa., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationApril 22, 1933, Serial No. 667,493 1 Claim. (Cl. 236.15)

My invention relates to temperature control apparatus and it hasparticular relation to automatic temperature regulating apparatus. 7

It is an object of my invention to provide tem-' perature responsiveapparatus that will instantaneously and continuously respond tovariations in temperature.

Another object of my invention is to provide temperature responsiveapparatus that shall automatically compensate for any variations from apredetermined temperature or temperature range.

Another object of my invention is to provide an electrical dischargedevice that is responsive to couple lies in the very tiny output ofelectrical energy therefrom which makes it rmsuitable for automatic use.According to my invention, I have devised a heat-responsiveelectron-discharge device that is continually responsive to a variationin heat, especially in the temperature range from 50 to 200 0., andwhose response to said temperature is an exponential function of theamount of heat. My invention eliminates the contact mechanisms 10 of thethermostats and it has the distinct advantage over the usualthermo-couple in the fact that the output of the tube can be amplifiedwith great ease to actuate the automatic control of the heat. source ofheat for the medium.

Another object of my invention is to provide an In Fig. 1, I havedisclosed a preferred system electrical discharge device having anenvelope of of control of a furnace or bath utilizing altergood thermalconducting material "and having a nating current in accordance with myinvention. ,material emitting electrons in response to heat The furnaceor bath 10 has a source of heat 11 on the inside of the good thermalconducting matherefor which may be an electrical heat produc- 2o terialof the envelope. ing coil. Directly immersed in this furnace or Anotherobject of my invention is to provide a bath is an electron dischargedevice 12 diagramheat-responsive electron discharge device immaticallyillustrated therein but whose preferred mersed in the medium whosetemperature is to be form is disclosed in Fig. 3. This electrondiscontrolled, said electron discharge device having charge device hasananode 13 therein and a electrical connections therefrom forautomatlcathode 14 either within the tube or as a part of callycontrolling the temperature of the medium. the envelope havingheat-responsive electron- Other objects of my invention will becomeeviemitting material thereon. Connections '15 and dent from thefollowing detailed description. 16 lead from the electron dischargedevice to the taken in conjunction with the accompanying automaticcontrol apparatus preferably located 3 drawing, in which: v on theexterior of the furnace or bath. This ex- Figure l is a diagrammaticview of a system of terior control system preferably has a battery 17control of a furnace or bath organized in accordto maintain a potentialdrop across the electrodes ance with the present invention and usingalterand an alternating-current interrupter 18 which nating current; pis preferably GO-cycle. Fig. 2 is a diagrammatic view of a system of Anysuitable amplifier means may be used, such control similar to that ofFig. 1, except that dias is diagrammatically indicated by the numeralrect-current is used; and l9, and this may be associated as desired by aFig.3 is a cross-sectional view with certain portube 20 and suitablecondenser 21, and resistancetions in elevation of my preferred form ofheatmeans 22 in addition to the usual transformer responsive electrondischarge device. means 23. A power tube 24 is also illustrated,

One of the difficulties with the usual thermoconnected between theamplifier means and the stats for controlling the temperature of amedium temperature control means, per se, which is indisuch as a furnaceor bath, is that the thermostat cated by the numeral 25.

has an off-and-on position that requires contacts It is to be noted thatthe circuit connected to and the consequent damage and noise caused bythe electron discharge device is illustrative of one the arcs and clicksin moving from one position type of means for amplifying the output fromthe to another. Furthermore, these thermostats necelectron dischargedevice 12 and is not to be reessarily require a wide range oftemperature begarded as limiting the broad idea of the invention. tweentheir minimum and maximum tempera- While many devices might be used forcontrolling the heating current in the coil 11 in response to theamplified signal from the electron discharge device 12, I haveillustrated one preferred form of apparatus, but I do not intend to havethe invention regarded as limited thereto. A small tures of the medium.They are very unsuitable for automatic use where the medium must be keptat one particular temperature, and not vary from this temperature to anyextent.

A distinct disadvantage of the usual thermoalternating-current motor 26is connected tothe output of the power tube 24 and has its armaturesynchronous with the So -cycle interrupter 18. A resistance device 27 isconnected to the armature of the alternating-current motor 26 to exertopposition to the torque of the motor, which torque is illustrated bythe arrow 28, pointing in a clockwise direction. The armature is alsoconnected through-suitable bearings with an arm 29 acting as a contactarm in the resistance 30 connected in the heating circuit 31 of theheating coil 11 of the furnace or bath. The heating circuit 31 is, ofcourse, connected to a suitable source of heating current 32. The fieldof the small alternatingcurrent motor 26 is illustrated at 33.

'The furnace or bath and the control system attached thereto are, ofcourse, designed for automatically maintaining the furnace or bath at acertain temperature. Of course, it is within the skill of the usualelectrical engineer to provide means for shifting the system so that thefurnace or bath may be set at any desired temperature.

The heating coil 11 will heat up the furnace or bath until the amount ofheat affects the heat responsive device 12. As the amount of heat in-.

creases, there will be a greater increased output from the electrondischarge tube because its response is a logarithmetic function of theamount of heat. This increased current is amplified by theamplifyingsystem and produces more current through the field coil 33 of thealternating-current motor 26 and increases the torque 28 of the motor,so that it overcomes the opposition of the resistance device 27 andmoves the resistance arm 29 clockwise to place more resistance in theheating circuit 31 and so decrease the amount of heat supplied by theheating coil 11 of the furnace or bath. Byproper design, this responsecan be made instantaneous to any increase in the amount of heat of themedium and-decrease also instantaneously the amount of heat supplied tothe medium.

If the amount of heat in the furnace or bath decreases below the desiredamount, then the current from the electron discharge device willdecrease, with the result that the current through the field 33 of themotor 26 will decrease, the torque 28 will lessen so that the resistancedevice 27 will move against the torque of the armature and shift the arm29 counter-clockwise to cut out part of the resistance 30 and soincrease the amount of current through the coil 11, and thereby increasethe amount of heat supplied to the furnace or bath 10.

In Fig. 2, I have disclosed a similar system utilizing direct current inplace of alternating current. It will be noted that this system also hasthe battery 7, suitable resistance 22 and one or more tubes 24 connectedto the direct-current electrical coil 11 in the motor 34 for controllingthe heat supplied by the furnace or bath.

My heat responsive electron discharge device may take any one of manyforms. .I have discovered that a cathode having an electron material ofcaesium and'preferably in the form of its compound caesium-oxide, isespecially suitable to become electron-emitting in response to heatsupplied in the temperature range of about 50 C. and upwards. Otheralkali metals and their compounds may be used in place of or inconjunction with saesium and its compounds. For the higher temperatures,quartz is preferably used for the insulating parts of the envelope.

In Fig. 3, I have disclosed an electron discharge device in a form whichis especially suitable to make a quick response to a change in the heator temperature of the surrounding medium. The insulating part of theenvelope 40 is sealed to a material 41 having a good thermalconductivity, such as copper. This copper is coated on the inside with amaterial that is electron-responsive in regard to heat, such as caesiumoxide 42. On the interior of the tube is the anode 43 which isillustrated as supporting the pellet 44 that contained the caesium priorto its being flashed on the surface of the copper 41. If the medium isnot electrically conducting, then contact can be made to the exterior ofthe copper anode 41 by means of the connection 45 disclosed, and anotherconnection 46 can be made .to the anode 43. If, however, the medium isapt to provide leakage of currents, then the connections to the electrondischarge device can be covered with an electrically insulating butthermal conducting material. The copper anode 41, however, has theadvantage that it is not only thermally conducting, but is more suitablefor sealing in the insulating part of the tube, such as the glass orquartz portions 40.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many, modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claim.

I claim as my invention:

Apparatus for controlling temperature of a

